The features returned are in a scale where the x-height has been normalized to live in the region y = [-0.25 .. 0.25]. Example ranges for English below are based on the Linux font collection on 2009-12-04:

Params[CharNormY]

The y coordinate of the grapheme's centroid.

English: [-0.27, 0.71]

Params[CharNormLength]

The length of the grapheme's outline (tiny segments discarded), divided by 10.0=LENGTH_COMPRESSION.

English: [0.16, 0.85]

Params[CharNormRx]

The radius of gyration about the x axis, as measured from CharNormY.

English: [0.011, 0.34]

Params[CharNormRy]

The radius of gyration about the y axis, as measured from the x center of the grapheme's bounding box.